Long-term Archive And Notary C. Wallace Services (LTANS) Orion Security Solutions Internet-Draft U. Pordesch Expires: March 22, 2005 Fraunhofer Gesellschaft R. Brandner InterComponentWare AG September 21, 2004 Long term archive service requirements draft-ietf-ltans-reqs-02.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 22, 2005. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract In many scenarios, users need to be able to prove the existence of data at a given time and integrity of data, especially digitally signed data, in a common and reproducible way after an arbitrarily long period. This document specifies the technical requirements for a long-term archive service to support such scenarios. Wallace, et al. Expires March 22, 2005 [Page 1] Internet-Draft Long term archive service requirements September 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. General Principles . . . . . . . . . . . . . . . . . . . . . . 6 4. Technical Requirements . . . . . . . . . . . . . . . . . . . . 7 4.1 Enable submission, retrieval and deletion of archived data objects . . . . . . . . . . . . . . . . . . . . . . . 7 4.1.1 Functional Requirements . . . . . . . . . . . . . . . 7 4.1.2 Rationale . . . . . . . . . . . . . . . . . . . . . . 8 4.2 Provide evidence records . . . . . . . . . . . . . . . . . 8 4.2.1 Functional Requirements . . . . . . . . . . . . . . . 8 4.2.2 Rationale . . . . . . . . . . . . . . . . . . . . . . 8 4.3 Support Demonstration of Data Integrity . . . . . . . . . 8 4.3.1 Functional Requirements . . . . . . . . . . . . . . . 8 4.3.2 Rationale . . . . . . . . . . . . . . . . . . . . . . 8 4.4 Operate per a long-term archive policy . . . . . . . . . . 8 4.4.1 Functional Requirements . . . . . . . . . . . . . . . 9 4.4.2 Rationale . . . . . . . . . . . . . . . . . . . . . . 9 4.5 Data confidentiality . . . . . . . . . . . . . . . . . . . 9 4.5.1 Functional Requirements . . . . . . . . . . . . . . . 9 4.5.2 Rationale . . . . . . . . . . . . . . . . . . . . . . 9 4.6 Data and evidence transferability . . . . . . . . . . . . 9 4.6.1 Functional Requirements . . . . . . . . . . . . . . . 10 4.6.2 Rationale . . . . . . . . . . . . . . . . . . . . . . 10 4.7 Supporting Groups of Data . . . . . . . . . . . . . . . . 10 4.7.1 Functional Requirements . . . . . . . . . . . . . . . 10 4.7.2 Rationale . . . . . . . . . . . . . . . . . . . . . . 10 5. Operational Considerations . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13 A. Application scenarios . . . . . . . . . . . . . . . . . . . . 15 A.1 Archive service supporting long-term non-repudiation . . . 15 A.2 Pure long-term non-repudiation service . . . . . . . . . . 15 A.3 Long-term Archive Service as part of an internal network . . . . . . . . . . . . . . . . . . . . . . . . . 15 A.4 Long-term Archive External Service . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . 16 Wallace, et al. Expires March 22, 2005 [Page 2] Internet-Draft Long term archive service requirements September 2004 1. Introduction Digital data durability is undermined by continual progress and change on a number of fronts. The useful lifetime of data may exceed the life span of formats and mechanisms used to store the data. The lifetime of digitally signed data may exceed the validity periods of public-key certificates used to verify signatures or the cryptanalysis period of the cryptographic algorithms used to generate the signatures. Technical and operational means are required to mitigate these issues. A solution must address issues such as storage media lifetime, disaster planning, advances in cryptanalysis or computational capabilities, changes in software technology and legal issues. A long-term archive service aids in the preservation of data over long periods of time through a regimen of techinical and procedural mechanisms designed to support claims regarding a data object. For example, it might periodically perform activities to preserve data integrity and the non-reputability of data existence as well as ensuring the availability of data. Examples of periodic activities include refreshing timestamps or transferring data to a new storage medium. A long-term archive service may be used to support validation of the existence of documents, or assertions of agreements, originally asserted with digital signatures. Validation may occur at times in the future well beyond the validity period of the private key originally used to generate the signature, or even the validity of the algorithms available for digital signatures, message digesting or data encryption. A long-term archive service may be located within an enterprise network, communicating with local storage mechanisms and other applications, or a long-term archive service may be implemented as an external service accessible via an internet. A long-term archive service may use functionality, e.g. time stamping, provided by independent service providers. A primary goal of a long-term archive service is to support the credible assertion of something that is currently asserted at points well into the future. A long-term archive service may support a range of applications, including: wills, land records, medical data, criminal case files, personnel files, contracts. A long-term archive service may be used by any type of entity, e.g. organizations, citizens, notaries. Examples of long-term archive service usage by submitters include: Wallace, et al. Expires March 22, 2005 [Page 3] Internet-Draft Long term archive service requirements September 2004 - A company stores contracts using a third party service - A hospital stores medical data using an internal service - An individual wants to generate evidence of data possession at a particular point in time, e.g. for intellectual property purposes or endorsement of a contract - A law enforcement officer wants to store criminal data such that integrity of the data can be demonstrated years later For each of the above examples, there is a corresponding example involving retrievers, e.g. a company retrieves a contract in the case of a dispute or a law enforcement officer prepares information for a criminal trial. This document addresses the technical requirements for a long-term archive service. The requirements for long-term notarization services will be covered by a separate draft. Wallace, et al. Expires March 22, 2005 [Page 4] Internet-Draft Long term archive service requirements September 2004 2. Terminology Arbitrator: Principal for whom the validity of archived data characteristics, e.g., origin, integrity or time of existence, must be demonstrated. Archivation period: The period during which an archived data object is preserved by a long-term archive service. Archived data object: Data unit to be preserved by a long-term archive service. Archive package: Collection of information including archived data objects and associated evidence record. Evidence: Information that may be used to demonstrate the validity an archived data object or related attestations. Evidence record: Collection of evidence compiled for one or more archived data objects. An evidence record may include acknowledgements from a LTA, timestamps and verification data, such as public-key certificates, revocation information, trust anchors, policy details and role information. Long-term archive policy: A named set of rules that define operational characteristics of a long-term archive service. Long-term archive service (LTA): A service that is responsible for preserving data for long periods. Originator: Principal who produces, and possibly signs, an archived data object.The Originator does not necessarily have any relationship with a long-term archive service or any awareness of an evidence record associated with the archived data object. Retriever: Principal who retrieves an archived data objects and/or evidence record from a long-term archive service. Submitter: Principal who submits data objects for archiving. Timestamp: A signed attestation generated by a Time Stamping Authority (TSA) that a data item existed at a certain time. [RFC3161] specifies a structure for timestamps and a protocol for communicating with a Timestamp Authority (TSA). Time Stamping Authority (TSA): A service that generates timestamps. Wallace, et al. Expires March 22, 2005 [Page 5] Internet-Draft Long term archive service requirements September 2004 3. General Principles A long-term archive service may accept any type of data for preservation, including digitally signed data, encrypted data, time stamped data, data that has not been the subject of any cryptographic processing, textual data or images. A long-term archive service may preserve archived data objects as opaque collections of bytes with the primary aim being demonstration of data integrity. A long-term archive service does not operate upon evidence related to the content of archived data objects. Content-focused operations, including data format migration or translation, may be performed by a notary or notarization service. A long-term archive service preserves archived data objects over arbitrarily long periods of time. A long-term archive service provides material needed to demonstrate the existence and integrity of data objects. Wallace, et al. Expires March 22, 2005 [Page 6] Internet-Draft Long term archive service requirements September 2004 4. Technical Requirements This section describes requirements for a long-term archive system. 4.1 Enable submission, retrieval and deletion of archived data objects 4.1.1 Functional Requirements A long-term archive service must permit clients to perform the following basic operations: - submit data and receive an acknowledgement or proof of deposit - retrieve archived data objects, - delete archived data objects/terminate archivation period for an archived data object. Submitters must be able to specify an archivation period. It should be possible to extend the archiving period after the initial submission. Submitters should be able to specify metadata that, for example, can be used to enable retrievers to render the data correctly. Following submission, the service must provide a value that can be used to retrieve the archived data and/or associated evidence. It may be possible to retrieve archive packages by using a hash value of an archived data object. Deletion requests must be authorized and an authorization policy must be defined and observed by the long-term archive service (as part of an archive policy). In some cases, deletion may not involve physical deletion and instead may simply be an early termination of the archivation period. It must be possible to authenticate requests and responses, e.g. to enable LTAs to render an authorization decision. This may be accomplished using transport security mechanisms. The format for the acknowledgements must allow the identification of the archiving provider. The format for the acknowledgements must allow the identification of the participating client. The LTA must provide an acknowledgement, or proof of deposit, that permits the submitter to confirm the correct data was accepted by the LTA. This proof need not be provided immediately. Wallace, et al. Expires March 22, 2005 [Page 7] Internet-Draft Long term archive service requirements September 2004 4.1.2 Rationale Submission, retrieval and deletion of archived data objects are necessary basic functions of a long-term archive service. 4.2 Provide evidence records 4.2.1 Functional Requirements A long-term archive service must be capable of providing evidence records to support the long-term non-repudiation of data, e.g. in the case of legal disputes. It must be possible to submit data along with previously generated evidence, i.e. to support transfer of data from one archive to another. Submitters must be able to specify metadata that, for example, can be used to provide enable retrievers to render the data correctly. 4.2.2 Rationale Supporting non-repudiation of data existence and origin is a primary purpose of a long-term archive service. Evidence may be generated by or otherwise obtained by the service providing them to a retriever. A long-term archive service need not be capable of providing all evidence necessary to produce a non-repudiation proof. In particular, trust anchors and algorithm security policies have to be provided by other services. 4.3 Support Demonstration of Data Integrity 4.3.1 Functional Requirements A long-term archive service must be capable of producing evidence that can be used to demonstrate the integrity of data for which it is responsible from the time it received the data until the expiration of the archivation period of the data. 4.3.2 Rationale Demonstration that data has not been altered while in the care of a long-term archive service is a first step towards supporting non-repudiation of data. Content-focused operations will be the function of a notarization service. 4.4 Operate per a long-term archive policy Wallace, et al. Expires March 22, 2005 [Page 8] Internet-Draft Long term archive service requirements September 2004 4.4.1 Functional Requirements A long-term archive service must operate per a long-term archive service policy that defines characteristics of the implementation of the long-term archive service. The policy may define characteristics such as the quality of timestamps obtained or generated by the long-term archive service or triggers for preservation activities, e.g. timestamp refresh or data format migration. A long-term archive service must be able to provide information identifying the policies in use at any point in time. Submitters must be able to indicate the archive policy under which the submitted data should be handled. The service must provide an indication of the archive policy observed by the service. If a long-term archive service does not support a client-requested policy, it must return an error indication. 4.4.2 Rationale Similar to a certificate policy, a long-term archive policy provides a shorthand means of technically expressing a set of rules that govern operation of a long-term archive service. 4.5 Data confidentiality 4.5.1 Functional Requirements A long-term archive service must provide means to ensure confidentiality of archived data objects, including confidentiality between the submitter and the long term archive service. Standard encryption algorithms and formats, e.g. AES and CMS, should be supported. The concept should be open to add other methods for confidentiality, like sharing secrets between different archive providers. Encryption or other methods must not pose a risk to evidence. 4.5.2 Rationale Individuals may wish to use the services of a commercial long-term service without disclosing data to the commercial service. 4.6 Data and evidence transferability Wallace, et al. Expires March 22, 2005 [Page 9] Internet-Draft Long term archive service requirements September 2004 4.6.1 Functional Requirements A long-term archive service must support the transfer of archived data objects, evidence and evidence records from one service to another. 4.6.2 Rationale Before the end of an archived data object's archivation period, a long-term archive service may cease operation. In such cases, it must be possible for the archived data object (and any associated evidence) to be transferred to another service that will continue preservation of the data until the end of the archivation period. 4.7 Supporting Groups of Data 4.7.1 Functional Requirements The service should support groups of data objects. Submitters should be able to indicate which data objects belong together, i.e. comprise a group. Retrievers should be able to retrieve all members of a group of data objects. It should be possible to provide evidence for groups of archived data objects. For example, it should be possible to archive a document file and a signature file together such that they are covered by the same evidence record. Where an LTA operates upon groups of data objects, non-repudiation proof must still be available for each archived data object separately. 4.7.2 Rationale In many cases data objects belong together. Examples include: - a document file and an associated signature file, which are two separate objects - TIF-files representing pages of a document - a document file and an evidence file (possibly generated by another LTA or notary service) In these cases, it is to the best advantage to handle these data objects as a group. Wallace, et al. Expires March 22, 2005 [Page 10] Internet-Draft Long term archive service requirements September 2004 5. Operational Considerations A long-term archive service must be able to work efficiently even for large amounts of archived data objects. In order to limit expenses and to achieve high performance, it may be desirable to minimize the use of trusted third parties, e.g. LTA operations should be designed to limit the number of timestamps required to provide the desired level of service. Necessity to access archived data objects should be minimized. It may only be necessary access to the archived data objects if the archived data objects are requested by users or if hash algorithms used for indexing or evidence record generation become insecure. Wallace, et al. Expires March 22, 2005 [Page 11] Internet-Draft Long term archive service requirements September 2004 6. Security Considerations Data is the principal asset protected by a long-term archive service. The principle threat addressed by a long-term archive service is undetected loss of data integrity. Certificate revocation could retroactively invalidate previously verified signatures. Measures may be implemented to support such claims by an alleged signer, e.g. collection of revocation information after a grace period during which compromise can be reported or preservation of subsequent revocation information. When selecting access control mechanisms associated with data stored by a LTA, the lifespan of the archived data object should be considered. For example, the credentials of an entity that submitted data to an archive may not be available or valid when the data needs to be retrieved. During lifespan of an archived data object, formats may cease to be supported. Software components to process data, including content or signatures, may no longer available. This could be a problem particularly if non-standard formats are used or proprietary processing is employed. The submitter should take care to avoid this potential problem. For example, the submitter could periodically retrieve data, convert the data and re-submit it in new format. Of course additional mechanisms, applications or tools are needed in order to conserve evidence value. Other specifications of LTANS, in particular to notary services will address these problems. Some applications may require processing of a chain of archive policies present in an evidence record, e.g. to ensure that compatible policies were used throughout the lifetime of an archived data object. Wallace, et al. Expires March 22, 2005 [Page 12] Internet-Draft Long term archive service requirements September 2004 7. Acknowledgements Thanks to members of the LTANS mailing list for review of earlier drafts and many suggestions. 8 References [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [RFC2028] Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process", BCP 11, RFC 2028, October 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3029] Adams, C., Sylvester, P., Zolotarev, M. and R. Zuccherato, "Internet X.509 Public Key Infrastructure Data Validation and Certification Server Protocols", RFC 3029, February 2001. [RFC3161] Adams, C., Cain, P., Pinkas, D. and R. Zuccherato, "Internet X.509 Public Key Infrastructure Time-Stamp Protocol (TSP)", RFC 3161, August 2001. Authors' Addresses Carl Wallace Orion Security Solutions Suite 300 1489 Chain Bridge Road McLean, VA 22101 Fax: +1(703)917-0260 EMail: cwallace@orionsec.com Ulrich Pordesch Fraunhofer Gesellschaft Dolivostrasse 15 Darmstadt, Germany D-64293 EMail: ulrich.pordesch@zv.fraunhofer.de Wallace, et al. Expires March 22, 2005 [Page 13] Internet-Draft Long term archive service requirements September 2004 Ralf Brandner InterComponentWare AG Otto-Hahn-Strabe 3 Walldorf, Germany 69190 EMail: ralf.brandner@intercomponentware.com Wallace, et al. Expires March 22, 2005 [Page 14] Internet-Draft Long term archive service requirements September 2004 Appendix A. Application scenarios Below are several example application scenarios demonstrating one or more of the basic service features mentioned above. A.1 Archive service supporting long-term non-repudiation A long-term archive service may store data objects, like signed or unsigned documents, for authenticated users. It may generate time stamps for these data objects and obtain verification data during the archivation period or until a deletion request is received from an authorized entity. A.2 Pure long-term non-repudiation service A long-term archive service may only guarantee non-repudiation of existence of data by periodically generating time stamps and obtaining verification data. It stores data objects (e.g. documents and signatures) locally only for the purpose of non-repudiation and does not function as a document archive for users. It does not support retrieval and deletion of data objects. A.3 Long-term Archive Service as part of an internal network A long-term archive service may be part of an enterprise network. The network provider and archive provider may be the same institution. In this case, the provider will use an external TSA, to generate non-repudiation evidence from a third party. An internally generated acknowledgement would be worthless. A.4 Long-term Archive External Service A long-term archive service may be provided over the internet for enterprises or consumers. In this case, archiving and providing evidence (via time-stamps or other means) may be adduced by one organisation and its own technical infrastructure without using external services. Wallace, et al. Expires March 22, 2005 [Page 15] Internet-Draft Long term archive service requirements September 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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